Question

I was looking around online and found a class to use ArrayLists in Stack operations. After looking up the arraylist I noticed the <E> designation there too. I followed it all the way back to Collection and I don’t understand what the <E> would be in this example:

public class MyStack<E> {
   private ArrayList<E> arrList;

   public MyStack() {
       arrList = new ArrayList<E>();
}

   public void push(E item) {
       arrList.add(item);
}

... more methods...
}

What does “E” refer to? If it was explained in the docs I either missed it or just don’t understand it.

Answer 1

<E> represents the type of data that you will use in your Stack. The simple example will be enough:

MyStack<String> myStack = new MyStack<String>();
myStack.push("Sample string");

This is called Java Generics